1. Field of the Invention
The present invention relates generally to catalyst monitoring in a motor vehicle and, more particularly, to a method and apparatus for monitoring catalyst efficiency in a catalytic converter, such that step response characteristics of the catalyst as measured by an oxygen sensor linearly correlate to catalyst efficiency.
2. Discussion
Catalytic converters are used to reduce major air pollutants, such as hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NO.sub.x), contained in the exhaust gas from an internal combustion engine of a motor vehicle. Each converter contains catalysts that produce a heated chemical reaction that transforms noxious pollutants into less harmful carbon dioxide (CO2) and water (H.sub.2 O) vapors. A catalytic converter is integrated downstream from the vehicle's engine into the vehicle's exhaust system. The effectiveness of reducing pollutants by a catalytic converter is highly dependent on the temperature and total gas throughput which, in turn, depends on the operational states and conditions of the internal combustion engine. Over time, catalyst efficiency degrades and thus decreases the capacity of the converter to convert toxic material. Government environmental regulations require continued reductions in vehicle emissions as well as accurate monitoring of various components of the emissions system.
Therefore, it would be desirable to provide a repeatable and robust method of monitoring catalyst efficiency in a catalytic converter. Catalyst monitoring should be performed with minimal processing requirements and no additional sensors or circuitry other than that provided by a typical motor vehicle. In addition, it should provide a less intrusive means of monitoring catalyst efficiency such that the algorithm output linearly correlates to the catalyst efficiency as measured by an oxygen sensor.